feat: conf inherit (#2568)

* feat: add ValuerWithParent

* feat: make etcd config inherit from parents

* chore: add more tests

* chore: add more tests

* chore: add more comments

* chore: refactor

* chore: add more comments

* fix: fix duplicated code and refactor

* fix: remove unnecessary code

* fix: fix test case for removing print

* feat: support partial inherit

core/mapping/fieldoptions.go

@@ -8,6 +8,7 @@ type (
 	// use context and OptionalDep option to determine the value of Optional
 	// nothing to do with context.Context
 	fieldOptionsWithContext struct {
+		Inherit    bool
 		FromString bool
 		Optional   bool
 		Options    []string
@@ -40,6 +41,10 @@ func (o *fieldOptionsWithContext) getDefault() (string, bool) {
 	return o.Default, len(o.Default) > 0
 }
 
+func (o *fieldOptionsWithContext) inherit() bool {
+	return o != nil && o.Inherit
+}
+
 func (o *fieldOptionsWithContext) optional() bool {
 	return o != nil && o.Optional
 }